Most of the Internet applications today require multicasting. For example, software updates, multimedia content distribution, interacting gaming and stock data distribution require multicast services. All of these applications require privacy and authenticity of the participants. Most of the multicasting groups are dynamic and some of them are large in number. Only those users who belong to the multicasting group should receive the information and be able to decrypt it. New users joining the group should receive information immediately but should not understand the information that was released prior to their joining. Similarly, if users leave the group, they should not receive any further information and should not be able to decrypt it. Keys need to be distributed to the users belonging to the current session and hence some kind of key management is required. Existing schemes for secure multicasting are limited to small and static groups. To allow large and dynamic groups to use the services of multicasting, some protocols have been developed: Multicast Trees, Spanning Tree, Centralized Tree-Based Key Management, Flat-key Management and Distributed Key Management. Some of these schemes are better than others with respect to the speed, memory consumption, and amount of communication needed to distribute the keys. All these schemes are limited in performance with respect to the speed, memory consumption, and amount of communication needed in distributing the keys. In this thesis, a number of public and private key algorithms and key management techniques for secure and dynamic multicasting are studied and analyzed. The thesis is focused on the secure lock method developed by Chiou and Chen, using the Chinese Remainder Theorem. The protocol is implemented for a small group of users and its performance is studied. While, the secure lock method works well for a small group of users and the performance is degraded when the group grows in size. A protocol is proposed for a large and dynamic group, based on the idea of the Chinese Remainder Theorem. A performance study is carried out by comparing our proposed protocol with the existing multicasting protocols. The analysis shows that the proposed protocol works well for large and dynamic groups and gives significantly better performance. / Master of Science